1. Field of the Invention
The present invention relates to a method for producing carbon black. More particularly, the present invention relates to a method for producing carbon black, by an oil furnace method, wherein small size particle carbon black is obtained with a high yield.
2. Discussion of the Background
An oil furnace method for producing carbon black is usually conducted in a furnace comprising a first reaction zone, where fuel is burned by air or an oxygen-containing gas which generates a high temperature atmosphere necessary for the heat decomposition of a feedstock hydrocarbon, a second reaction zone situated adjacent to said first reaction zone, where a feedstock hydrocarbon is introduced to said high temperature atmosphere to induce a carbon black producing reaction, and a third reaction zone situated downstream of said second reaction zone, where a cooling medium is introduced to stop the carbon black producing reaction.
As the cooling medium used in the above described process, a water spray is usually used because of ease of handling and high cooling effect, and no other cooling medium has been actively used.
For example, in Unexamined Japanese Patent Application Laid-Open (KOKAI) No. Heisei 7-102185 (1995), nitrogen-enriched air is introduced between a feedstock hydrocarbon spraying point and a cooling point but the object of introducing nitrogen-enriched air is to control the quality of carbon black, and the final cooling is conducted, by water, as conventionally done. No method for cooling other than that using the water is described or suggested in this publication.
The object of the present invention is to optimize the cooling medium used in the third reaction zone, and the way of introducing this cooling medium to obtain small size particle carbon black.
The present inventors have conducted studies on the cooling medium and the way of introducing it into the furnace to solve the above problems, and found that unexpectedly, cooling by a gaseous medium is advantageous for obtaining higher yields than conventionally obtained when water is used. Namely, the present inventors conducted studies using various kinds of reaction stopping media, and found that although cooling by water has advantages such that it can be easily conducted, it has also disadvantages such that the gasification of carbon black which lowers a carbon black yield, is increased. The present inventors presumed that this is because, in the neighborhood of the water introducing point, the water vapor concentration becomes high, and the temperature condition in the cooling process increases reactions that gasify carbon black such as a water gas reaction. Also the present inventors inferred that stopping the carbon black producing reaction with water causes a delay in vaporization of water droplets and problems on mixing efficiency with a high-temperature gas from the second reaction zone, which consequently causes unevenness of reaction stopping.
The present inventors also found that, by introducing the cooling medium vertically to the axial direction of the furnace, a reaction stopping effect can be improved, consequently small size particle carbon black is obtained in high yield, and they attained to the present invention.